1. Field of the Invention
The present invention relates to a laminated ceramic condenser, and more particularly to a dielectric ceramic material for compensation of temperature used in a laminated ceramic condenser using a base metal as an inner electrode.
2. Background Art
Laminated ceramic condensers are widely used as electronic part of small size, high capacity and high reliability, and a large number of laminated ceramic condensers are used in one electronic device. With the recent tendency of miniaturizing the size of devices and enhancing the performances thereof, there is an increasing desire for further miniaturized size, enhanced capacity, lowered price and improved reliability of laminated ceramic chip condensers.
Usually, a laminated ceramic condenser is manufactured by laminating an inner electrode layer paste and a dielectric layer paste by the method of sheeting or printing and sintering them simultaneously.
When the dielectric materials which have been used in prior laminated ceramic condensers are sintered in a reductive atmosphere, they are reduced to give a semiconductor. Thus, a noble metal such as Pd has been used as a material of inner electrode, because such a noble metal does not melt at the sintering temperature of dielectric ceramics and is not oxidized even if sintered under a high oxygen partial pressure enough to prevent the conversion of dielectric ceramics into semiconductor. However, noble metals such as Pd are expensive, which has obstructed the reduction of cost and enhancement of capacity of laminated ceramic condensers.
Currently, the use of relatively inexpensive base metals such as Ni and Ni alloys is being studied. If a base metal is used as the conductive material of inner electrode layer, the inner electrode layer is oxidized when sintered in the atmospheric air. Accordingly, the simultaneous sintering of dielectric layer and inner electrode layer must be carried out in a reductive atmosphere. However, if sintering is carried out in a reductive atmosphere, the dielectric layer is reduced as has been mentioned above and thereby the specific resistance is lowered. Thus, non-reductive dielectric materials have been proposed.
Laminated ceramic condensers using a non-reductive dielectric material, however, is disadvantageous in that lifetime of insulating resistance (IR) is shortened and reliability is deteriorated when the thickness of dielectric layer is decreased to 5 .mu.m or less.
As non-reductive dielectric ceramic material, JP-A-126117/1988, JP-A-289709/1988 and JP-A-217426/1993 have disclosed those prepared by adding silica, lithium glass, lithium silicate+alkaline earth fluoride, boron-lithium glass and the like to a (CaSr) (TiZr)O.sub.3 type dielectric ceramic composition so as to make possible a simultaneous sintering with a base metal such as Ni, Cu or the like.
However, the dielectric ceramic condensers using the aforesaid material are disadvantageous in that:
(1) those prepared by adding Li type glass or CaF+Li.sub.2 SiO.sub.3 type glass show a frequency dependence in dielectric constant and dielectric loss tangent (tan .delta.), and especially marked increases in dielectric constant and dielectric loss tangent are observed at a high temperature exceeding 100.degree. C. and at a low frequency of several hundreds Hz. Further, those prepared by adding Li glass are short in the accelerated lifetime of IR and low in reliability when the dielectric layer is made into a thin layer; PA1 (2) those prepared by adding SiO.sub.2 are short in the accelerated lifetime of insulating resistance and low in reliability when thickness of dielectric layer is decreased; etc. PA1 (1) A non-reductive dielectric ceramic material comprising a main component and auxiliary components, wherein when said main component is represented by the following formula: EQU [(Ca.sub.X Sr.sub.1-X)O].sub.m [(Ti.sub.Y Zr.sub.1-Y)O.sub.2 ] PA1 0.ltoreq.X.ltoreq.1, PA1 0.ltoreq.Y.ltoreq.0.10, and PA1 0.75.ltoreq.m.ltoreq.1.04 PA1 0.ltoreq.Z.ltoreq.1, and PA1 0.5.ltoreq.V.ltoreq.4.0. PA1 (2) The non-reductive dielectric ceramic material of Paragraph (1), which further contains at least one oxide of rare earth elements (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu) including Sc and Y or Nb, Mo, Ta and Ti in an amount of 0.02 to 1.5 mol %. PA1 (3) The non-reductive dielectric ceramic material of Paragraph (1) or (2), wherein the sintering temperature is not higher than 1,300.degree. C. PA1 (4) The non-reductive dielectric ceramic material of any one of Paragraphs (1) to (3), wherein the mean crystal grain diameter is not greater than 3 .mu.m. PA1 (5) A laminated ceramic condenser having the non-reductive dielectric ceramic material of any one of Paragraphs (1) to PA1 (4) as a dielectric material. PA1 (6) The laminated ceramic condenser of Paragraph (5), wherein difference between temperature coefficient .tau.C of capacitance determined from C25 (capacitance at 25.degree. C. at 1 MHz) and C125 (capacitance at 125.degree. C. at 1 MHz) according to: EQU .tau.C(ppm/.degree. C.)={(C125-C25)/C25}.times.{1/(125-25)}.times.10.sup.6 PA1 (7) The laminated ceramic condenser of Paragraph (5) or (6), wherein the accelerated lifetime until insulating resistance (IR) reaches 2.times.10.sup.5 .OMEGA. or less under a direct current electric field of 70V/.mu.m at 200.degree. C. is no less than 100 hours. PA1 (8) The laminated ceramic condenser of any one of Paragraphs (5) to (7), which has an inner conductor containing at least nickel.
In addition, it is required currently to develop a dielectric ceramic composition for compensation of temperature having a small temperature-response of capacitance and controllable arbitrarily in the range of -150 to +150 ppm/.degree. C., and it is necessary today to develop a ceramic material capable of providing such a controllable condenser having a low temperature constant.